Cooling screen with variable tube diameter for high gasifier power

ABSTRACT

A liquid-cooled cooling screen for an entrained-flow gasifier for gasification of fuels in dust or liquid form using a gasifier agent containing free oxygen, at pressures between atmospheric pressure and 8 MPa and gasification temperatures between 1200 and 1900° C. The liquid-cooled cooling screen of which the cooling pipes in the central cylindrical section have thinner walls than the cooling pipes in the lower and upper conical sections. A cooling screen design has sufficient strength under high pressure difference over the cooling screen wall, a pipe wall thickness which ensures reliable operation of the cooling screen and high heat throughput, and pressure equalization between the cooling screen gap and the reaction chamber under all operating circumstances.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2017/071574 filed Aug. 28, 2017, and claims the benefitthereof. The International Application claims the benefit of GermanApplication No. DE 10 2016 216 453.8 filed Aug. 31, 2016. All of theapplications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to an entrained-flow gasifier for the gasificationof solid and liquid fuels at temperatures between 1200 and 1900° C. andpressures between atmospheric pressure and 10 MPa (100 bar), whereinsolid fuels are coals of different rank which are ground to fine dust,petroleum cokes or other solid carbon-containing materials, and liquidfuels can be oils or oil-solids suspensions or water-solids suspensions,using a free oxygen-containing oxidation agent, in which gasifier acooling screen 8 arranged in a pressure shell 15 delimits a reactionchamber 9.

BACKGROUND OF INVENTION

In entrained-flow gasifiers, the thermally highly loaded reactionchamber 9 is formed by a cooled tube construction. This construction,the so-called cooling screen 8, as a whole is pressure-stable only to alimited degree, with the tubes per se being configured to bepressure-resistant. The cooling screen 8 is positioned in a pressurevessel 15. For reasons of thermal stability of the pressure container, acertain distance between the pressure container and cooling screen isnecessary. The thus resulting backspace 10 (also referred to as coolingscreen gap) is flushed with an inert gas and has pressure equalizationin relation to the reaction chamber, with the result that, in normaloperation, equal pressure prevails in the reaction chamber and in thebackspace.

Since pressure changes in part constitute highly dynamic processes, itmust be ensured that pressure equalization can occur in each operatingstate and that, as a result of a flow directed into the reactionchamber, the penetration of reaction gas and dust into the coolingscreen gap 10 is limited. In addition, the cooling screen as a wholemust have a certain minimum resistance to pressure differences over itswall. This minimum resistance to pressure differences decreases with anincreasing cooling screen diameter and cooling screen height, andtherefore this problem is intensified with an increasing gasifier power.Furthermore, the cooling screen is exposed to a high thermal loadingand, in order to avoid damage, good heat transfer from the reactionchamber into the cooling water is required. This requirement can beachieved by small tube wall thicknesses, this in turn counteracting thedifferential pressure resistance of the cooling screen.

The prior art presents gasifier values of 500 MW, as described, forexample, in DE 197 181 31 A1. In the design described therein, a coolingscreen which consists of cooling tubes welded in a gastight manner issituated within a pressure vessel. This cooling screen is supported onan intermediate base and can freely expand upward. This ensures that,upon the occurrence of different temperatures on the basis ofstarting-up and shutdown operations and resultant change in length, nomechanical stresses occur which could possibly lead to destruction. Toachieve this, there is no fixed connection at the upper end of thecooling screen but rather an annular gap between the cooling screencollar and the burner holder flange that ensures free movability and isfilled with elastic, thermally resistant fiber mats. These mats are notconfigured to be gastight and thus allow a dry, condensate-free andoxygen-free gas to flow behind the cooling screen gap. This flushing isintended to prevent hot gasification gas from flowing back into thecooling screen gap upon pressure fluctuations. A disadvantage with thisconfiguration is that these mats are positioned in the annular gap onlyin a form-fitting manner and can be forced out of the guide underrelatively high differential pressures. Consequently, the mats no longerperform their function of limiting the dust transfer from the reactionchamber into the backspace, which ultimately means that reaction gas anddust pass into the cooling screen gap 10 in spite of oppositely directedflushing. The dust and gasification gas transfer into the backspaceresults, on the one hand, in corrosion occurring on the rear side of thecooling screen or of the pressure shell, which can lead to destructionin the long term, and, on the other hand, the entry of dust into thecooling screen gap 10 also causes an increased CO concentration, afterswitching off the gasifier, within the reaction chamber and thegas-channeling downstream systems. Inspection and possible repair isthus greatly delayed for safety-related reasons.

Alternatively, the gap, as described in DE10 2007 045 321 and DE10 2009005 856, can be closed by means of a corrugated tube compensator. Inthis configuration, the flushing gas is channeled from the coolingscreen gap 10 into the reaction chamber via an additionalpressure-equalizing line connected to the combination burner, in orderthereby to ensure the necessary pressure equalization between thecooling screen gap and reaction chamber. A disadvantage with thissolution is the high price of compensators of relatively large diameterand the additional amount of tubing required for the pressure-equalizingline.

In order to protect the cooling screen at high gasification temperaturesand to limit the thermal loading, the cooling screen design described inDE 197 181 31 requires a sufficient layer consisting of liquid and solidslag on the cooling screen. It has been found in practice that this slaglayer can form a different thickness depending on the coal used or itsash. As a result thereof, the input of heat into the cooling screen andthe amount of heat to be removed therefrom can greatly increase and leadto wall temperatures above the admissible material values and torelatively high thermal wear.

In order to avoid damage to the cooling screen in these cases, what isrequired is a smaller tube wall thickness, but this, on the other hand,leads to smaller admissible pressure differences over the cooling screenwall. This admissible pressure difference is decreased further with anincreasing gasifier power, since here the reaction chamber diameter and,associated therewith, the cooling screen surfaces are also increased andresult in lower strength values. A remedy to this is provided by alarger tube wall thickness, but this counteracts the goal of a lowerwall thickness, reduces the heat transfer and reduces the amount of heatwhich can be removed. An increased tube wall thickness causes greatertemperature differences between the tube inner side and tube outer side,with the result that additional stresses are induced in the tube wall.Both aspects, higher stresses and higher thermal wear, lead topotentially shorter service times of the cooling screen. Consequently,owing to the contrary effect of a changed tube wall thickness, the areaof application and the performance of the cooling screen are limited tostrength of the cooling screen versus amount of heat which can beremoved.

SUMMARY OF INVENTION

The problem on which the invention is based is to specify a technicalsolution for the discussed, mutually conflicting requirements.

The problem is solved by an object having the features of the claims.

The invention makes use of the finding that, through a correspondingburner configuration, the temperature release can be set such that alower thermal loading can be realized in the conical regions of thecooling screen.

The solution according to the invention to the problem lies in a coolingscreen configuration with sufficient strengths under high pressuredifference over the cooling screen wall and a tube wall thickness whichensures a reliable operation of the cooling screen and a high heattransfer; also provided is a pressure equalization between the coolingscreen gap 10 and reaction chamber 9 in all operating states.

Advantageous developments of the invention are specified in thesubclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below by way of figuresas an exemplary embodiment to an extent that is required forunderstanding. In the figures:

FIG. 1 shows an 8-flight cooling screen according to the inventionhaving 4 feet distributed uniformly over the circumference, and

FIG. 2 shows a configuration according to the invention with 8 bearingplates and 32 flushing and pressure-equalizing tubes distributedthereon.

In the figures, identical designations designate identical elements.

DETAILED DESCRIPTION OF INVENTION

According to the invention, thin-walled tubes 5 are used in the regionof the highest temperature loading, that is to say the cylindrical partof the cooling screen, and, in order to ensure the mechanical strength,thick-walled tubes 3 are used in the conical regions of the coolingscreen (at the top and bottom), in particular for the purpose of takingup the bending moments through intrinsic load and under differentialpressures which occur.

The tubes are furthermore chosen such that the tube outside diameter iskept constant over the entire cooling screen height 8 and the tube wallthickness is varied only over the tube inside diameter. The transitionfrom the smaller to the larger tube inside diameters is here configuredto be smooth via a gradual diameter increase 4 in order thus to avoidthe creation of “wake areas” in which, owing to discontinuous flowconditions, sufficient cooling cannot be ensured. The maintenance of auniform outside diameter of the cooling screen tubes leads to ahomogeneous configuration of the cooling screen. In addition toproduction-related advantages (for example automatic welding), the thusensured uniform tampability of refractory material is particularlyadvantageous.

To further increase the mechanical strength of the cooling screen, themechanical load of the cooling screen is dissipated into the enclosingpressure shell 15 via feet 1, thereby further reducing the bendingmoments overall and thus fundamentally increasing the admissiblepressure difference. However, the feet 1 provided simultaneously causelocal stress peaks. For this reason, the wall thickness transitions 4described are, as far as possible, positioned for outside thedisturbance region of the feet (region in which local stress peaks canoccur by the feet in the presence of mechanical loading). Whilemaintaining a region of thinner wall thicknesses 5 that is, as far aspossible, large, the wall thickness transitions 4 are arrangedvertically above the feet and, as viewed tangentially, centrally betweenthe feet 1.

With a symmetrical configuration of feet, the following formula for thehorizontal arrangement of the wall thickness transitions can be used forpositioning the wall thickness transitions 4 in the lower cylindricalregion:

$\gamma = \frac{\text{?}}{n_{P}*k \times z}$?indicates text missing or illegible when filed

where

γ=angle between the center of the foot and the wall thickness transition(7),

n_(P)=number of feet and

${k =^{\begin{matrix}n_{R} \\n_{F}\end{matrix}}},$

where n_(R)=number of cooling screen tubes.

Symmetrical configuration means that always the same number of wallthickness transitions is arranged between the feet, that is to say k isan integral number.

The vertical distance x between the foot and the first wall thicknesstransition is chosen such that at least one further tube with a largewall thickness is situated between the uppermost tube connected to thefoot and the tube having a wall thickness transition. Here, the foot isadvantageously configured such that at least three tubes in the conicalregion and three tubes in the cylindrical part are fixedly connected toeach foot. With an additional fastening of the foot to the upper tubesof the lower conically configured cooling screen part, the load take-upof the cooling screen can be configured to be particularly advantageous.

In the upper region of the cooling screen, the thick-walled tubes areused in the conical part and continued into the cylindrical part to suchan extent that at least one cooling screen tube achieves half arevolution in the cylinder. A further increase in the cooling screenstrength is possible by an optimization of the upper and lower conicalcooling screen part in association with an increase in the setting angle16. However, since, on the other hand, this increase in the settingangle leads to an increase in the cooling screen gap 10, the amount ofgas to be removed upon emergency depressurization of the reactor 9increases. With the flushing and pressure-equalizing lines 13 remainingthe same, an increased amount of gas in turn increases the pressuredifference over the cooling screen and counteracts an increase in thestrength by a larger setting angle. Therefore, in an advantageousconfiguration, an angle 16 of between 35° and 60° is chosen. In theexemplary embodiment of FIG. 2, this angle 16 is chosen to be 45°.

FIG. 1 represents an exemplary embodiment with eight cooling screentubes (8-flight cooling screen) and 4 feet distributed uniformly overthe circumference. The vertical distance has been chosen to be four tubediameters and the horizontal distance has been chosen to be 22.5°.

In spite of the described active measure for increasing the admissibledifferential pressure over the cooling screen wall, the admissibledifferential pressure in gasifiers of relatively large output (and hencevolume) is less than in the case of relatively small gasifier powers ofup to, for example, 500 MW, which means that further measures arenecessary in order to ensure secure operation without accumulation ofcoal dust in the cooling screen gap or corrosion of the pressurecontainer 15 or of the rear side of the cooling screen 8. It is ensuredin terms of construction that there is made available, in each operatingstate, a sufficiently large flow-traversed area for pressureequalization, but without allowing unhindered dust and reaction gasentry into the backspace of the cooling screen. For this purpose, metalflushing and pressure-equalizing tubes 12 are positioned in theexpansion gap of the cooling screen in such a way that, on the one hand,the admissible pressure difference over the cooling screen wall is notexceeded and that, on the other hand, the vertical thermal expansion ofthe cooling screen remains ensured. For the purpose of preventing dusttransfer, the necessary gap remaining for expansion is filled withflexible, thermally stable ceramic fiber mats 11. For the arrangement ofthe metal tubes over the circumference, bearing plates 13 are positionedat the upper termination of the cooling screen, with the number of thesebearing plates being chosen such that they correspond to the number ofcooling screen tubes. The metal tubes 12 are uniformly distributed onthese bearing plates, and the remaining annular space between thecooling screen termination and pressure container is sealed by means offiber mats 11 which are advantageously arranged above the tubes. Inorder to ensure a directed flow or to avoid backflows, a dry,condensate- and oxygen-free gas as flushing gas is introduced into thereaction chamber 9 via the nozzle 14 and the flushing andpressure-equalizing tubes 12.

FIG. 2 illustrates an exemplary embodiment with eight bearing plates and32 flushing and pressure-equalizing tubes distributed thereon.

The invention is also provided by a reactor for the gasification ofsolid and liquid fuels in the entrained flow at temperatures between1200 and 1900° C. and pressures between atmospheric pressure and 10 MPa(100 bar), wherein solid fuels are coals of different rank which areground to fine dust, petroleum cokes or other solid carbon-containingmaterials, and liquid fuels can be oils or oil-solids or water-solidssuspensions, using a free oxygen-containing oxidation means, wherein thereactor has a cooling screen 8 and a pressure shell 15, wherein acooling screen 8 delimits a reaction chamber 9 in a pressure shell 15,the cooling screen is configured with a plurality of tubes which arewound in parallel and through which a cooling liquid flows, the coolingscreen tubes have wall thickness changes with a thicker wall thicknessin the lower and upper region and a thinner wall thickness in thecentral cylindrical region, and the setting angle of the conical coolingscreen region has an angle 16 of 35° to 60°.

The present invention has been explained in detail for illustrativepurposes on the basis of specific exemplary embodiments. Here, elementsof the individual exemplary embodiments may also be combined with oneanother. The invention is therefore not intended to be restricted toindividual exemplary embodiments, but rather restricted only by theappended claims.

LIST OF REFERENCE SIGNS

Key:

-   1 Foot-   2 Thick-walled cooling screen tube connected to foot-   3 Thick-walled cooling screen tube-   4 Wall thickness transition of the cooling screen tube-   5 Thin-walled cooling screen tube-   6 Vertical distance between foot and wall thickness transition-   7 Horizontal distance between foot and wall thickness transition-   8 Cooling screen-   9 Reaction chamber-   10 Cooling screen gap-   11 Fiber mats-   12 Flushing and pressure-equalizing lines-   13 Bearing plate for flushing and pressure-equalizing lines-   14 Flushing connection in the pressure container-   15 Pressure container-   16 Setting angle of the conical cooling screen part-   17 Conical cooling screen portion at the lower end of the cooling    screen-   18 Cylindrical cooling screen portion

1. An entrained-flow gasifier for the gasification of fuels in dust orliquid form using a free oxygen-containing gasifying agent at pressuresbetween atmospheric pressure and 8 MPa and at gasification temperaturesbetween 1200 and 1900° C., comprising: a reaction chamber connected to aquenching chamber arranged therebelow via a guide pipe in a pressureshell, a cooling screen, wherein the reaction chamber is delimited bythe cooling screen, a gasification burner configured to be arranged atthe upper end of the reaction chamber, wherein a cooling screen gapbetween the cooling screen and pressure shell is flushed with an inertgas, wherein the cooling screen is configured by the winding of a numberof cooling screen tubes through which a cooling liquid flows, whereinthe cooling screen has a tapering conical cooling screen portion at theupper end, a tapering conical cooling screen portion at the lower endand a central cylindrical cooling screen portion therebetween, whereinthe cooling screen tubes are configured as a thick-walled cooling screentube in the region of the lower and the upper cooling screen portion andas a thin-walled cooling screen tube in the region of the centralcooling screen portion.
 2. The entrained-flow gasifier as claimed inclaim 1, wherein a setting angle of the conical cooling screen portionhas an angle of 35° to 60°.
 3. The entrained-flow gasifier as claimed inclaim 1, wherein the cooling screen is supported by feet which are eachfixedly connected to at least three tube windings of the conical coolingscreen portion at the lower end and to three tube windings in thecylindrical cooling screen portion situated thereabove.
 4. Theentrained-flow gasifier as claimed in claim 1, wherein an outsidediameter of the cooling screen tube is constant and the transition fromthe thick-walled cooling screen tube to the thin-walled cooling screentube is configured to be smooth in an inner part of the cooling screentube.
 5. The entrained-flow gasifier as claimed in claim 3, wherein thetransition from the thick-walled cooling screen tube to the thin-walledcooling screen tube is arranged in a horizontal direction between thefeet, and at least one thick-walled cooling screen tube is arrangedabove the foot in a vertical direction.
 6. The entrained-flow gasifieras claimed in claim 1, wherein the thick-walled cooling screen tube iscontinued into the cylindrical cooling screen portion to such an extentthat at least one cooling screen tube achieves half a revolution in thecylindrical cooling screen portion.
 7. The entrained-flow gasifier asclaimed in claim 1, wherein the cooling screen is configured with aplurality of tubes which are wound in parallel.
 8. The entrained-flowgasifier as claimed in claim 1, wherein flushing and pressure-equalizingtubes are arranged at an upper end of the cooling screen.
 9. Theentrained-flow gasifier as claimed in claim 8, wherein the flushing andpressure-equalizing tubes bear on bearing plates and the remaining gapis sealed with fiber mats.
 10. The entrained-flow gasifier as claimed inclaim 9, wherein each bearing plate is connected to a cooling screentube.
 11. The entrained-flow gasifier as claimed in claim 7, wherein thecooling screen is configured with eight tubes which are wound inparallel.